Telephone system with automatic ringing and automatic busy



I H. D. CURR'IER AND H. W. BRYCE.

TELEPHONE SYSTEM WITH AUTOMATIC RINGING AND AUTOMATIC BUSY.

' APPLICATION FILED JUNE II. 1915.

5%,891. I Emma @CII 5,1920,

2 SHEETS-SWEET H. D. CUHR-IER AND H. W. BRYCE.

TELEPHONE SYSTEM WITH AUTOMATIC RINGING AND AUTOMATIC BUSY. APPLICATIONFILED JUNE H, 1915.

1,354,891 A Patented; 00$. 5, 1920,

Z SHEETSSHEET 2.

EZZQZ TZEQ A A-AA l @WA UNITED-STATES PATENT" OFFICE.

-HIRAM D. CURRIER, 0F CHIUAGO, AND HARRY W. BRYCE,.OF DOWNERS GROVE,ILLI- NOIS, ASSIGNORS TO KELLOGG: SWITCHBOABD AND SUPPLY COMPANY, OFCHICAGO, ILLINOIS, A CORPOBATION OF ILLINOIS.

Specification of Letters Patent.

Patented Oct. 5, 1920.

I Application filed. June 11, 1915. Serial No. 33,628.

To all whom it may concern Be it known that we, HIRAM D. Cunnmn andHARRY W. BRYCE, citizens of the United States of America, residing inChicago, county of Cook, and Downers Grove, Dupage county, respectively,in the State of Illinois, have invented certain new and usefulImprovements in Telephone Systems with Automatic Ringing and Automatic-Busy, of which the following is a specification. Y

Our invention relates to telephone systems and has to do moreparticularly with manually operated trunk or link circuits which areemployed for interconnecting telephone lines, one of the features of ourinvention being the provision of an improved circuit arrangement bywhich no preliminary test of the called line is required by the B ontrunk operator. To this end, means is provided which automaticallyadjustsitself to bring about the automatic ringing of the calledsubscriber if the called line is idle, or if the called line is busy totransmit an audible busy signal to the calling subscriber and at thesame time to flash the supervisory lamp at the A operators position tonotify her of the busy condition of the called'line.

Another feature of our invention is the provision of means whereby aftera connection has been established to the called line, the application ofringing current to the said called line is dependent upon the operativeassociation of the A operators link circuit with the trunk or Boperators circuit. While still another feature of our invention is theprovision of improved means for flashing the calling supervisory lamp atthe A operators position when the trunk or B operator establishesconnection with a busy called line, thus eliminating any specialoperation on the part of the B o erator in transmitting a busy signal'tothe or originating operator. These and other objects of our inventionwill be more articularly pointed out in the ensuing spec' cation and.

in the appended claims.

For a better understanding of our invention, reference may be had to theaccompanying drawings in which I Figure 1 illustrates one embodiment ofour invention as applied thereto, and

Fig. 2 illustrates another embodiment of our mvention adapted for fourparty ringl teferring now more in general to our invention asillustrated in the accompanying drawings, and referring to Fig. 1, inwhich we illustrate our inventlon operating in connection with a singleparty ringing, we show a calling substation A of a well-known typeterminating at the exchange in a twowire common battery line circuit Lcomprising a line relay LR, a cut-off relay G0, a line signal S and themultiple jacks J.

A cord circuit C is shown associated with the line circuit L, andcomprises an answering plug P, and a calling plug P the two plugs beingconnected by the heavily marked conductors, and having the condensers Kand K interposed. The calling plug P is adapted for connecting tomultiple jacks of cord circuit comprises a calling tip supervisory relayCT and a calling sleeve supervisory relay CS, the two relays CT and CScontrolling the callin supervisory lamp CL. A.listening key L is alsoshown which when thrown connects the operators set 0 to the cordcircuit. An orderwire key OW is provided for connecting the operatorsset 0 with the trunk operators set 0 at the distant exchange so that theA operator at the cord circuit C may communicate with the operator atthe trunk circuit T. The trunk jacks J are located at the A operatorsposition and are connected by the heavily marked conductors 1 and 2 tothe trunk circuit T.

The trunk circuit T comprises a calling plug P connected to a repeatingcoil R. The'repeating coil R having the condensers K and Kinterposedbetween its windings 3 and 5 and 4: and 6. A relay 7 of highresistance is associated with'the incoming end of the trunk circuit Tand energizes when i I wanted substation;

' the trunk circuit T, we show the test control relays TC and TC therelay TC operating each time the plug 2 is inserted into a ack of acalled line, and the relay TC automatically adjusts itself dependingupon whether the line is in an idle or busy condition. A busy tonegenerator ET is provided which produces a busy tone that 15 heard by thecalling subscriber and also brings about the flashing of the supervisorlamp CL of the A operators cord circuit to notify her of the busycondition of the called line. The tgp and sleeve supervisory relays CTand C 1 are operated upon the response of the called subscriber. Therelay CT upon ener izing shunts out the hi h resistance relay whichallows the relay T of the cord circuit C to operate to eflace thesupervisory signal CL of the said cord circuit to notify the A operatorthat the called subscriber has answered. A ringing lockout relay BL isprovided which operates when the relay 7 restores-and interrupts thecircuit of the relay RC which in turn opens the circuit ofrelay RIthereby cutting ofl the ringing generator G. A link control relay trunkcircuit T as shown illustrates our in-.

LC is also provided as is also a test control shunt relay TCS. Theoperation of these relays in conjunction with the other apparatus willbe hereinafter more fully described.

The substation D- as shown at the called end of the trunk circuit T issimilar to that of the substation A and its associated line circuit Lexcept that it is of the three-wire common battery type. It comprisesthe usual line relay LE cut-off relay CO multiple 'acks J 2 and the linesignal S Re errin now in general to Fig. 2, the

-vention applied to four party ringing. We employ substantially the sameapparatus with theaddition of a party line ringing Rey RK and four rin'ing current generators G G G G of difi erent frequencies for signalingthe correspondingly tuned bells at .the substations on the party lines.The apparatus of Fig. 2 bears the same reference numerals as that ofFig. 1, but with difl'erent suflixes added.

Having described in general the apparatus which is embodied in ourinvention, we will now describe more in detail the operation of at thecircuit. as illustrated in Fig. 1.

Assuming that the subscriber at the substation A initiates a call bytheremoval of his receiver from its switch-hook an enerizing circuit fortheline relay Lllis estabished traced from battery through the windingof said relay, normal contact 8 ofrelay C through the substation to oundat normal contact 9 of relay CO. %pon the energization of relay LR, itsalternate contact 10 is closed bringig about the lighting of the linelamp S. e operator noting the lighted'signal S, inserts the plug P intothe jack J of the calling line, establishing a series energizing circuitfor the cut-0E relay C0 of line circuit L and the answering sleevesupervisory relay AS of the cord circuit C. This circuit extends frombattery through the winding of the relay AS, the sleeve contacts of theconnected plu and jack, through the winding of the relay 0 to ground.The relay CO upon energizing, opens the circuit of relay LR at contact 8allowing the relay LR to restore to efi'ace the line signal S. Theanswering tip supervisory relay AT is also energized over a circuittraced from battery, through the winding of relay AS the sleeve contactsof the connected plug and jack, alternate" contact 8 of relay CC,through the'substation, alternate contact 9 of relay CO, tip contacts ofthe connected plug and-jack. and through the winding of relay AT toground. The energization oi relay AT and relay AS prevents the lightingof the answering supervisory lamp AL. The operator now throws thelistening key LK to connect her operators set C to the cord circuit andinquires the wants of the calling subscriber. I

Assuming nowthat the calling subscriber at A desires connection with thesubstation D, the operatordepresses the orderwire key OW leading to theexchange in which the line of substation D terminates, to connect heroperators set 0 with that of the operators set 0 associated with thetrunk circuit T. The A-operator of the cord circuitC repeats the numberof the called subscriber to the operator of the trunk circuit T and theoperator at the trunk circuit T then assigns the trunk to be used by theA-operatcr. The A-operator then inserts the plug P into the trunk ack Jthus bringing about the energization of the calling sleeve supervisoryrelay CS over a circuit traced from battery through the winding of therelay CS, sleeve contacts of the plug P and jack J through the impedancecoil 11 to ground. The closing of the alternate contact 12 of relay CSbrings about the glowing of the calling supervisory lamp CL. The closingof the alternate contact 13 of relay CS establishes an energizingcircuit for the high resistance relay 7 of the trunk circuit T, tracedfrom permit sufiicient current flow throughthe relay CT of the cordcircuit C to cause it'to energize, thus pern itting the supervisory lampCL to remain lighted until the called subscribed at the substation D.answers. Upon the energization 0f the relay 7, a circuit for thesupervisory relay SR is estab lished, traced from battery, through thewinding of the said relay, to ground at alternate contact 14 of relay 7.Upon the energization of the relay SR, its alternate contact 15 isclosed, thereby closing a circuit for the supervisory lamp SS, tracedfrom battery through the said lamp SS, the alternate contact 15 of relaySR to ground at normal contact 16 of relay 17. If the trunk operator hasnot yet plugged into the jack of the called line the lighting of thesupervisory signal SS indicates to the trunk operator that the operatorat, the originating exchange has plugged into the assigned' trunk jack,while if the operator at the originating exchange has plugged into atrunk jack other than that of jack J (the jack of the as signed trunk),the lamp SS fails to light due to the failure of the relay 7 toenergize.

The operator of trunk circuit T having obtained the number of the calledsubscriber from the A-operator, inserts the trunk plug P 'intothe jack J2 of the Wanted line, without any preliminary testing, and assuming thatthe called line is idle, an energizing circuit for the cut-ofi" relay C0of the line circuit L and the test control relays TC and T0 of the trunkcircuit T are established, traced from ground through the winding of thecut-off relay CO the sleeve contacts of the jack J 2 and plug P throughthe winding of the relay TC and through the upper windin of the relay TCto battery. The relay T upon energizing, closes its alternate contact 18thereby closing an energizing circuit for the relay 17, traced frombattery through the winding of the said relay to ground at alternatecontact 18 of relay TC. The closing of alternate contact 18 of relay TCalso closes a circuit for relay TCS traced from battery through thewinding of said relay, normal contact 28 of relay RC to ground atalternate contact 18, but this operation of relay TCS is only incidentalat this time. The opening of normal contact 16 of relay 17 opens theenergizing circuit of the supervisory signal SS, bringing about itsefiacement. The relay T0 upon energizing, closes its alternate contact19, thereby establishing a locking circuit for itself, traced frombatterv through the lower winding of the said relay, its alternatecontact 19 to ground at alternate contact 16 of relay 17. The closin ofthe alternate contact 20 of the relay TC establishes a circuit for thelink control relay LC traced from battery through the winding of saidrelay to ground at alternate contact 20. The energization of the relayLC'brings about the closing of its alternate contacts 21 and 22, therebyestablishing the continuity of the talking strands to allow the ringingcurrent to be sent out over the line to the called substations signalbell. The closing of the alternate contact 16 of relay 17 alsoestablishes an energizing circuit for the relay RC, traced from batterythrough the winding of the said relay, the normal contact 23 of relayRL, normal contact 36 of relay CS and to ground at alternate contact 16of relay 17 The closing of the alternate contact 2 1 of relay RCestablishes an energizing circuit for the ringing interrupter relay I,traced from battery through the interrupter I, the winding ofinterrupter relay RI, alternate contact 25 of the relay LC, conductor26, alternate contact 24 of relay RC to ground at alternate contact 27of rela SR. The opening of contact 28 of relay 0 opens the circuit ofthe relay TCS. The relay RI is thus intermittently energized anddele'nergized and opens and closes its alternate contact 29 therebyconnecting ringing current from the generator G to the called line, saidringing current being traced from the ungrounded pole of the generatorG, alternate contact 29 of relay RI, the alternate contact 21 of relayLC, the tip contacts of the plug 1? and jack J through the condenser andcall bell of the called substation, the ring contacts of the connectedjack and plug, the alternate contact 22 of relay LC, the alternatecontact 30 of RI and through the resistance 31 to ground. An audibletone of the ringing current is also sent out to the calling subscriberssubstation over-the conductor 32, through the alternate contact 33 ofrelay RC, winding 4 and winding 6, alternate contact 133, alternatecontact 134 of relay TC through the winding of relay CT to ground. Thetone is induced into the other winding of R and produces the audibletone to be heardby the calling subscriber. The call bell of the calledsubstation is thus intermittently rung until the called subscriberanswers.

'Upon the response of. the called subscriber, an energizing circuit forthe relays CS and GT is established, traced from battery through thewinding of the relay CS normal contact 30 of relay RI, alternate contact22 of relay LC, the ring contacts of the connected plug and jack throughrelay thezsubstation, the tip contacts of the jack and plug, alternatecontact 21 of relay LC, normal contact 29 of relay RI, through thewinding of relay CT to ground. The 010s ing of the alternate contact 31- of relay CT brings about the shunting of the hi h resistance relay 7allowing the relay T of the cord circuit C to operate through the nowclosed alternate contact 34 of the relay CT. The relay CT, uponenergizing, opens its'normal contact 35 to etlace the supervisory lampCL, notifying the A operator of the cord circuit 'C that the calledsubscriber at substation D has answered. The relay 7, restoring tonormal due to the said shunt, opens the energizing circuit of the relaySR, and the relay SR upon deenergizing, opens the energizing circuit forthe interrupter relay RI at its alternate contact 27, whereupon relay RIrestores preventing further application of ringing current to the calledline. The restoration of the relay' SR brings about the energization ofthe relay BL, traced from battery through the winding of the said relay,normal contact 37 of relay SR, alternate contact 36 of relay CS toground at alternate contact 16 of relay 17. Relay BL upon energizing,establishes a locking circuit for itself traced from battery through itswinding, its alternate contact 38 to ground at alternate contact 16 ofrelay 17. The opening of normal contact 23 of relay RL opens theenergizing circuit of control relay RC, and the closing of normalcontact 28 ofnRC again establishes the circuit for relay TCS. Thesubscriber at the calling substation A, and'the subscriber at the calledsubstation D are now in conversational circuit, the

said talking circuit being traced over the heavily marked conductors.

Assuming now that the subscribers have finished conversation, thesubscriber at the substation A replacing his receiver upon theswitch-hook, opens the circuit of the answering tip supervisory relay ATof the cord circuit C, and allows the relay to again close its normalcontact 50 to cause the supervisory lamp AL to glow. The subscriber atthe substation replacing his receiver upon the switch-hook opens thecircuit of the tip calling supervisory relay GT and the sleeve callingsupervisory relay CS of the trunk circuit T. The restoration of thecalling tip supervisory relay CT opens the shunt about the hlghresistance relay 7 due to the opening of contact 34 of relay CT,allowing said relay 7 to again energize. The relay 7 energizing againcauses the denergization of the calling ti supervisory relay CT of thecord circuit C thereby causing the glowing of the calling supervisoryrelay L. (The closin of the alternate contact 14, of: the again closesan energizing circuit neeaeei J ,-the energizing circuit of the high re-7 sistance relay 7 is interrupted, allowing the said relay to restore tonormal. The relay 7 restoring, opens'the circuit of the supervisoryrelay SR, the said relay restoring again closes the circuit for signalSS through normal contacts 15 of relay SR, 36 of relay CS to ground atcontact 16 of relay 17 notifying the trunk operator that the A-operatoras withdrawn the plug from the trunk jack. The operator at the trunkcircuit T now withdraws the plug P of the jack J of the calledlinethereby opening the energizing circuit for the test control relay T Therelay TC restoring to normal opens its contact 18 and thereby allows therelay 17 to restore to normal. The relay 17 restoriligLopens the lockincircuits for the relay and the relay C The relay TC restoring opensthe.circuit for relay LC. All the apparatus of the trunk circuit T isnow in its normal condition as is also that of'the cord circuit C, andtherefore the cord circuit C and the trunk circuit T are now availablefor establishing other connections.

Assuming now that the calling subscriber D is busy the operation of thecircuit is the same as previously described up to and including theinsertion of the plug P into jack J 2 of the called line. The operatorof the trunk circuit T, without any prelinrinary testing, inserts theplug P in the multiple jack of the called line, closing a circuit forthe relay TCv traced from ground through the sleeve contacts of themultiple jacks .and the connected plug through the windin of the relayTC, through the relay TC to ttery. The relay TC operates, but sufilcientcurrent does not flow through the winding of the relay. TC to bringabout its operation due to the fact that battery is connected throughanother cord circuit to the sleeve contact of a multiple jack of line D.The closing of the alternate contact 18. of relay TC establishes anenergizing circuit for the relay 17 traced from battery through thewinding of said relay to round at alternate'contact 18. of relay C, andalso closing an energizing circuitfor relay TCS as previously described.The closing of the alternate contact 16 of relay 1'7 closes anenergizing circuit for the relay RC, traced from battery through thewinding of the relay BC, normal contact 23 of rela RL and normal contact36 of rela C to round at alternate contact 16 0 relay 17..

nate contact 31. The opening and closing of the said alternate contact34 opens and closes the shunt about the high resistance relay 7 and thisenergization and denergization of the relay 7 brings about theenergization and denergization of the relay CT,

I of the cord circuit C. The said relay CT opening and closing itsnormal contact 35 causes the flashing of the calling supervisory lampCL, thus signaling the A- operator that the called subscriber is busy.The calling subscriber also receives a, busy tone ,which may be tracedfrom battery through busy tone interrupter BT, normal contact 52,alternate contact 133, winding 6 of R, condenser K winding 4 of R,alternate contact 33, through resistance 31 to ground. This tone isinduced into the wind ings 3, 5 of the repeating coil R to the waitingcalling subscriber which notifies him that the called line is busy. TheA-operator noting the flash busy signal, withdraws the plug 1 from thejack J bringing about the deenergization of the relay 7, the said relaydeenergizing opens the circuit for the sleeve supervisory relay SR,thereby allowing the relay SR to restore to normal and close the circuitof the supervisory signal SS thus notifying the trunk operator that theA operator has withdrawn the plug P from the jackv J The trunk operatornoting the lighted signal SS withdraws the plug P from the connectedjack and the apparatus restores as before described.

Should-a local operator test the multiple jack of the called line whileconversation is going on, the resulting ground from the test relay ofthe local cord circuit will assist in holding up the relay T0 of theconnected trunk circuit T from the sleeve of the jack and connected plugthrough the relays TC and TC to battery and not affect the circuit inany way. Again, should a local operator test while a second trunkcircuit T is in connection with a multiple jack of a busy line, groundfrom the test relay of the local cord circuit will flow from the sleeveof the multiple jack through'the tip of the plug of the second connectedtrunk circuit T through the winding of the relay TC of the secon trunkcircuit, at this point the circuit divides one branch extending throughthe upper winding of relay TC to battery, the other branch extendinthrough the normal contact 55 of relay OS of the second trunk throughthe resistance R to battery. The resistance B being lower than theresistance of the upper winding of relay TC suflicient current isshunted away from the relay TC to preventits operative energization,thereby preventin any interference with the trunk circuit that is in abusy condition transmitting a busy tone to the calling subscriber andflashing the A operators supervisory lamps.

Referring now more in detail to Fig. 2, we illustrate a trunk circuit Tembodying the features of our invention operating in connection with afour-party ringing sysdition,of the four party ringing ke RK Theoperation of the trunk circuit 1 as a whole, is practically the same aspreviously described. The operation of this circuit is practically thesame as previously described in connection with Fig. 1, up to andincluding the act of inserting the trunk plug P of the trunk circuit Tinto the jack of the called line. The operator 'having inserted the plugP of the trunk circuit T into a multiple jack of the called line, (notshown) a circuit is established for the test control relay TC and thetest control relay TC as previously described. The relay 17 is alsooperated by the actuation of the relay TC The relay TC operating closesa locking circuit for itself through the alternate con tact 16 of therelay 17 The closing of the alternate contact 20 of the relay TCestablishes an energizing circuit for the relay LC The operator afterhaving inserted the plug P into the jack of the wanted line, depressesthe proper ringing plunger of the partly line ringing key RK to connecttheproper generator frequency to ring the call bell of the calledsubstation. When the ringing 'key 'is in its fully depressed position,the end spring contact 60 assumes its alternate position, closing anenergizing circuit for the ringing control relay RC traced from batterythrough the wnding of the said relay, the alternate contact 60 of theend spring of the ringing key RK the normal contact 38 of relay RL toround at alternate contact 16 of relay 17 pon pressure being releasedfrom the actuated plunger it assumes its ringing position. The relay RCupon energizing forms a locking circuit for itself traced from batterythrough its winding, through its alternate contact 24;, normal contact38 of relay RL to ground at alternate contact 16 of relay 17 Anenergizin circuit for the ring'm interrupter relay R 1 is established uon t e closure of the alternate contact 7 6 o relay RG traced frombattery through the interrupter I through its own winding, alternatecontact 25 and alternate contact 76 to round at alternate contact 27 Therelay 1 is thus intermittently energized and deenergized by theinterrupter I. The call bell of the called subscriber is thusintermittently rung due to the energization and deenergization of therelay R1 whlch alternately connects and disconnects the ringing lead 61to the alternate contact 29 of relay R1 Upon the response of the calledsubscriber, the relays (/T and CS operate as previously describedbringing about the operation of the relay RL which then closes a lockingcircuit for itself through its contact 38 to ground at alternate contact16 The locking circuit for the relay RC is opened allowln it to restoreto normal. The opening 0 the alternate contact 7 6 of relay RCinterrupts the circuit of the interrupter relay RI thereby preventingfurther application of the ringing current to the called line. Thesubscribers having finished conversation replace their receivers andsignal for disconnect, the same as hereinbefore described. Therestoration of the apparatus of trunk circuit T is the same as that ofFig. 1. The testless features as described in Fig. "1 in which theoperator plugs into a called line without making preliminary tests isalso incorporated in the trunk T as illustrated.

It is thought that a further description ofthis trunk circuit isunnecessary.

In working out our invention we have shown it operating with aparticular form of link circuit but we contem late using it inconnection with other circuits than those shown and therefore weaio notdesire to be limited to the exact system as shown but aim to cover allsuch changes and modifications that come within the spirit and scope ofthe appended claims.

Having described our invention, what we claim as new and desire tosecure by United States Letters Patent, is:

l. A telephone system comprisin subscribers lines terminating in multipe terminals at the exchange, a trunk circuit provided with a manualconnection terminal for connecting to said lines as called lines, andapparatus responsive to the connection of said terminal to one of saidcalled lines and difi'erently operable according to the busy or idlecondition of the called line to automatically connect ringing current tothe said called line or to operate a flash supervisory signal accordingto such idle or busy condition.

2. A telephone system comprising subscribers lines terminating inmultiply connected jacks at the exchan e, an operator controlled linkcircuit provi ed with a plug terminal for connecting" with the jacks ofsaid lines and apparatus difierently operable upon the connection ofsaid plug terminal to one of said jacks according tothe busy or idlecondition of the line connected with to connect ringing current to saidline or to operate a flash su ervisory signal according to such idle orbusy condition.

3. A telephone system comprising subscribers lines terminating inmultiply connected jacks at the exchange, an operator controlled linkcircuit and an operator controlled manual trunk circuit forestablishingconnection between the jacks of said lines, a manual terminal for saidtrunk circuit, a signal for said link circuit, and automatic apparatusincluding a double-wound test relay automatically operable responsive tocircuit and a manual trunk circuit for establishing connection betweensaid jacks of callin and called lines, and apparatus responsive to theconnection of said trunk circuit to the 'ack of the called line anddifierentl opera le according to the idle or busy con 'tion of thecalled line whereby ringing current is connected to said line'or a flashsupervisory si al is operated according to such idle or nay condition,said apparatus including a double wound test relay.

5. A telephone system comprising sub--- scribers lines terminating inmultiply connected jacks at the exchange, a link circuitand a manualtrunk circuit for establishing connection, between said jacks of callingand called lines, a visual signal for said link circuit and automaticapparatus responsive to l the connection of said trunk circuit to a jackof the called line and dilferently operable according to the idle orbusy condition of the called line whereby ringing current is connectedto said line or said signal is operated according to such idle or busycondition,

6. A telephone system including telephone line, a trunk circuit providedwith a manually controlled plug terminal for connection thereto, meansfor automatically ringing a substation on said line'responsive to theconnection of said plug to said line, said means being inefl'ective ifsaid .line is busy upon connection made therewith, and means responsiveto the busy condition of subscribers line, a trunk circuit provided Awith a plug for connection thereto, a pair of relays for said trunkcircuit connected to a conductor of said plug, a visual si al for saidtrunk circuit, means controlle b the energization of said relays forautomatlcally associating ringing apparatus with the said called line,said relays being responsive to the connection of said plug with saidcalled subscribers 'line, and means controlled by one of said relays foraffecting an operation of said signal.

8. In a telephone system, a link circuit provided with a supervisorysignal, a trunk circuit provided with testing means adapted to bemanually connected to a called subscribers line, automatic ringing meanscontrolled by said testing means and responsive to the connection of thetrunk circuit to the calledsubscribers line for signaling the saidcalled subscriber, means controlled by the called subscriber foroperating the said supervisory signal, and means controlled by the saidautomatic testing means for flashing said supervisory signal if thecalled subscribers line'is busy.

9. In a telephone system, subscribers lines, an operators link circuitprovided with a supervisory lamp and an operators manually controlledtrunk circuit for interconnecting said telephone lines, automatictesting means for said operators trunk. circuit for distinguishingbetween idle and busy called subscribers lines, a manually controllableterminal for said trunk circuit for connecting the trunk circuit to thejack of the called subscribers line, thereby operatively associatingsaid automatic test means with the called subscribers line, ringingmeans automatically controllable by said testing means and responsive tothe connection of said trunk circuit to the called line for signalingsaid called subscriber, and

means responsive to said automatic testing means for intermittentlyoperating said supervisory lamp if the called subscribers line is busy.

10. In a telephone system the combination of an A-operators link circuitand a B-operators link circuit for establishing connection betweentelephone lines, automatic testing means for said B-operators linkcircuit for distinguishing between the idle and the busy condition of acalled subscribers line, means responsive to the idle condition of thecalled subscribers line upon the connection of the B-operators linkcircuit to the said called subscribers line and to the operativeassociation of the A-operators link circuit with the B-operators linkcircuit for controlling the application of ringing current to the saidcalled subscribers line, and a visual signal for said A operators linkcircuit responsive to a busy condition of the called subscribers line.

11. In a telephone system a calling subscribers line and a busy calledsubscribers line, an A-operators link circuit and a manuallycontrollable trunk circuit rovided with a plug terminal for connectlngsaid lines, automatic means responsive to the connection of said plugterminal to one of said called lines for ringing the called subscriber,a signal for said A-operators link circuit, automatic testing means forsaid trunk circuit responsive to the connection of the trunk circuit tothe said busy called subscribers line for intermittently operatin thesaid supervisory signal to-notify' the -operator of the busy conditionof the called line.

12. In a telephone system an A-operators link circuit and a B-operatorslink circuit for extending a call to a called subscribers line,automatic testing means for said B-operators link circuit, signalingapparatus for the B-operators link circuit, means controlled by theoperative association of the A and B link circuits and by the saidautomatic testing means for operatlvely associating the said signalingmeans with the called subscribers line, said means including a trunkrelay, bridged across the strands of said trunk circuit, and subscribercontrolled means for denergizing said relay.

13. In a telephone system an A-operators link circuit and a trunkcircuit provided with a manually controllable terminal for extending acall to a called subscribers line, a supervisory signal for saidA-operators link circuit, automatic testing means for said trunk circuitfor operating said supervisory signal or'for associating automaticringing link circuit and a B-operators trunk circuit for extending acall to a busy called subscribers line, a visual signal for saidA-operators link circuit, a relay bridged across the conductors of saidtrunk circuit, and means responsive to the connection of said trunkcircuit to said called subscribers line for shunting said relay wherebysaid visual signal is intermittently operatedto denote the busycondition of said called subscribers line.

15. A telephone system including a busy called subscribers line, a linkcircuit and a trunk circuit for extending a call to said subscribersline, a visual signal for said link circuit, a relay bridged across theconductors of said trunk circuit, and means responsive to the connectionof said trunk circuit necting circuit, ringing mechanism, and

- maticall 16' apparatus responsive to the connection of said plugterminal to said telephone line and difierently operable according tothe busy or idle condition of said line to-either autoconnect saidringing apparatus to said ine or to operate said visual signal accordingto such idle or busy condition.

- 17. A telephone system including a calling subscribers line and acalled subscriberfs line, a link circuit and a trunk circuit forconnecting said lines, a visual signal for said link circuit, ringingmechanism for said trunk circuit, apparatus differently operable toautomatically connect either said ringing mechanism to said calledsubscribers line or to operate said visual signalaccordin to the idle orbusy condition of the said ca ed subscribers line, and a plug terminalfor said trunkcircuit adapted. to be connected to said calledsubscribers line to operatively associate said apparatus with the calledsubscribers line.

18. A telephone system including a calling subscribers line and a calledsubscribers line, a link circuit and a trunk circuit for connecting saidlines in conversational circuit, a connection terminal for said trunkcircuit for manual connection to said called line, and apparatusassociated with said trunk circuit for either signaling the calledsubscriber or the link circuit operator according to the idle or busycondition-of said called line, said apparatus being operated re-'sponsive to the connection of said terminal to thesaid called line.

Si ned by us at Chicago, county of Cook and tate of Illinois, inthepresence of two witnesses.

HIRAM D. GURRIER.

HARRY W. BRYCE. Witnesses:

Gno. A. YANOCKOWSKI, M. R. ROCKFORD,

